Please help me get my pH up!

[stapet77]

We have had our tank for about 9 months now and everything is stabilizing nicely. We finally got our nitrates down to about 5, and Alk 5-6 meq/l, Mg 1200, Ca 400, temperature 77-78, salinity 1.024-1.025. However, every time we get our pH up to 8.3 using buffer, it drops overnight to 8.1 and does not go up again the next day. I realize it is normal for it to drop at night, but it never goes back up. According to SeaChem these values for Mg, Ca, and, Alk should be right on. Are there trace elements that could affect the pH? Is there anything else besides an ionic balance that could cause consistently low pH? We are using purigen, Phosorb, and deNitrate, and Stability (with water changes) - all by Sea Chem. These are the only other additives we use.

[sasquatch]

Thats rather beyond me but somebody will surely be along with answers, does the ph stay there or continue to drop? and what are you measuring with? Steve

[Whiskey]

Yep,.. I had the same problems as you, for me it was high CO2 levels in my house. Do this,.. take a cup of water from your tank,.. measure the PH,.. then take it outside and airate for an hour outside. Now check the PH again. If it goes way up you know that CO2 in your house is your problem too.

Whiskey

[prow]

i dont know that its CO2 causing his issue here. could be, but i would expect my ph to be on the low side with a alk level that high. really you dont want your ph to come up anymore at this point. if you raise the ph with the buffer you will raise your alk some too, you then run the risk of precipitions. i would just let it ride and cut out the buffer and keep your Ca where it is, you can use just the Ca part of your 2 part or just Ca to maintain levels. but no more alk or buffer. let things fall back to balance on there own.

give this a read here.
Calcium and Alkalinity by Randy Holmes-Farley - Reefkeeping.com

its a long read here is the part i am talking about, and so randy lives on

Solubility of Calcium Carbonate

In surface seawater, calcium carbonate is supersaturated (although in deep water it is undersaturated for reasons described in this link). That is, there is already more in solution than would form by trying to dissolve solid CaCO3 into the water. It also means that calcium and carbonate are poised to precipitate any time they are given the opportunity (e.g., appropriate seed crystals and a lack of crystallization inhibitors such as magnesium and phosphate).

The equilibrium constant for the dissolution and precipitation of calcium carbonate is shown below:

(3) K = [Ca++][CO3--]

When K exceeds a particular value (the Ksp), the water is supersaturated. If K is less than this value, then the water is undersaturated, and calcium carbonate solid in the water can dissolve. This relationship is normally defined using the supersaturation parameter, which is symbolized as W:

(4) W = [Ca++][CO3--]/Ksp

When W = 1, the solution is exactly saturated. When W exceeds one, it is supersaturated, and when W is less than 1, the solution is undersaturated.

In normal seawater, W ~ 3 for aragonite and W ~ 5 for calcite, though these values have been steadily dropping as carbon dioxide has been added to the atmosphere, reducing the seawater pH. Aragonite and calcite are just different crystal forms of calcium carbonate. Calcite is slightly more stable, and hence is slightly less soluble than aragonite (i.e., has a lower Ksp). Organisms can precipitate both aragonite (pteropods and corals) and calcite (foraminifera and cocoliths), but most of the precipitation in reef tanks is aragonite (although certain organisms such as abalone form both).

Reef tanks often have higher alkalinity and higher calcium than seawater, and hence are more supersaturated than seawater. In tanks with a high pH (such as many tanks using limewater) the supersaturation is also higher than in seawater. At the same alkalinity, if you raise the pH, you convert some of the bicarbonate into carbonate:

(5) HCO3 - + à CO3- - + H+

Within the pH range of most reef tanks (up to about pH 8.5 or so), the amount of carbonate present is approximately linear with the hydrogen ion (H+) concentration because of the relationship seen in equation (5). So if the pH rises from 7.5 to 8.5, there is approximately a ten-fold increase in the carbonate concentration. From pH 8.0 to 8.5, the increase in carbonate is about threefold.

Combining these various factors, here are some combinations of calcium, alkalinity, and pH that have equal supersaturation with respect to aragonite:


W = 1 (risky: dissolution of aragonite begins here)

pH = 7.7.......................pH = 8.2
Calcium = 410 ppm.........Calcium = 340 ppm
Alkalinity = 2.5 meq/L......Alkalinity = 1.0 meq/L

W = 3 (typical of normal seawater)

pH = 8.2.....................pH = 8.0....................pH = 8.4
Calcium = 410 ppm.......Calcium = 410 ppm.......Calcium = 260 ppm
Alkalinity = 2.5 meq/L....Alkalinity = 4.0 meq/L...Alkalinity = 2.5 meq/L

W = 6 (non-biological precipitation is more likely)

pH = 8.2.....................pH = 8.2
Calcium = 410 ppm.......Calcium = 820 ppm
Alkalinity = 5.0 meq/L...Alkalinity = 2.5 meq/L

pH = 8.0.....................pH = 8.7
Calcium = 410 ppm.......Calcium = 410 ppm
Alkalinity = 8.0 meq/L....Alkalinity = 2.5 meq/L

pH = 8.45
Calcium = 410 ppm
Alkalinity = 4.2 meq/L

[prow]

hey i have one more for ya this a good ref. also from randy. Chemistry and the Aquarium

and the zone your in.

Corrections for Zone 3

Zone 3 problems are a little harder to correct, and are fairly common. It is, in fact, the problem in the real question posed at the beginning of this article (it doesn’t say so there, but the alkalinity was 3.2 meq/L). This problem is typically caused by overdosing alkalinity RELATIVE to calcium, but does not necessarily imply that calcium is either too high or too low (though it is almost always too low). To correct problems in this zone, monitoring of calcium and alkalinity values during correction is especially important.

One more word about this zone before getting to solutions: Many tanks end up here because aquarists are trying to correct pH problems by adding “buffer.” In my opinion, one should not try to correct any pH problem by simply adding an alkalinity supplement. If you are low on alkalinity, it is a fine course of action to raise the alkalinity. But if alkalinity is OK, or even high, adding an alkalinity supplement to alter the pH may simply create a worse problem. Better solutions to pH problems are discussed in this recent article6.

If this problem is extreme (i.e., you are far from the line at the right hand edge of zone 3), then water changes may be the best way to correct to the problem. In most cases, however, water changes aren’t necessary.I would advise correcting this problem by adding a calcium chloride supplement until you have moved into the target zone (or zones 1 or 2 that you can then treat as described above) as shown in Figure 4. Almost any brand of calcium chloride will do (Kent Turbo Calcium, Kent Liquid Calcium, ESV, etc.). Certain other calcium supplements may also be OK (such as just the calcium component of the two-part calcium and alkalinity additive systems), but you do not want to add any alkalinity. You CANNOT use limewater or a calcium carbonate/carbon dioxide reactor to correct this problem. Any of the balanced calcium and alkalinity additive systems will move you parallel to the line at the edge of the zone, while you want to move over to it, and cross it.


Figure 4. A graph showing how to correct values within zone 3 by adding a calcium additive, such as calcium chloride (the blue arrow).

If calcium is less than 400 ppm, I’d suggest using this handy online calculator7 to determine how much dry calcium chloride is necessary to move back to the target zone. Note that it is a minimum estimate because it does not know how much alkalinity you have, so it cannot know if you are only raising calcium directly (which it calculates) or are also precipitating calcium carbonate (when alkalinity is high this will probably happen, but is typically not a problem other than that it uses up some of what you add).

If the calcium is above 400 ppm in this zone (unlikely, but it does happen), then you can safely either do nothing until it drops and you need to add more calcium, and treat it as suggested in the previous paragraph, or you can add some calcium immediately, move into zone 1, and then just let it drop on its own.